The goal of the proposed program is the development of a portable, reliable, and simple electromagnetic pump driver for pneumatically actuated blood pump systems. This driver eliminates compressors, pressure regulators, solenoid valves, sliding seals, or any components subject to mechanical wear. The basis of the design is an electromagnetically driven welded metal bellows. The total excursion and rate of movement of the bellows are electronically controlled using a closed-loop network which monitors bellows position and internal pressure. This microprocessor-based control system permits flexible operating modes including fixed rate, autonomous variable rate, passive synchronous, and EKG triggered synchronous counterpulsation at any desired stroke volume. It also allows for direct specification of the pressurization envelope to the blood pump, eliminating excessive systolic rates of pressurization or high diastolic negative pressures, either of which can produce hemolysis. By virtue of its extreme mechanical simplicity, the driver is inherently reliable. Its target electromechanical efficiency of 20% will also result in a compact and portable pump driver that is low in cost compared to the bulky or mechanically complex systems currently available.